Our long-range goal is to understand the transcriptional basis of energy homeostasis and how its alteration contributes to obesity and metabolic diseases. Brown fat is a tissue that is specialized in energy expenditure. It is present is adult humans and its activity is inversely associated with human obesity. Thus, brown fat is potentially an attractive therapeutic target tissue for obesity and metabolic diseases. We are interested in how brown fat development and function is regulated by the dynamics of histone methylation and demethylation. We found that promoters of a subset of brown fat genes are methylated at a specific lysine residue of histone H3 in preadipocytes and are demethylated during differentiation. We further identified a demethylase that is responsible for the demethylation during differentiation. We propose that this demethylase-catalyzed removal of histone methylation plays a key role in brown fat determination and metabolism. In the first aim, we will investigate in detail the roles of this demethylase, in particular its demethylation activiy, in brown fat gene expression and brown fat cell metabolism, and whether this demethylase is required for conversion of white adipocytes to brown adipocytes. In the second aim, we will investigate the mechanism by which this demethylase regulates brown fat determination and function. We will perform ChIP-seq to map the occupancy of both this demethylase and its substrate, which will provide us a genome-wide, mechanistic and functional view of this demethylase. In the third aim, we will investigate the in vivo role of this demethylase in brown fa metabolism through both transgenic mice and loss-of-functional studies.